Performance enhancing coating on intraluminal devices

ABSTRACT

This invention comprises guidewires, stents and other intraluminal devices having a performance enhancing coating deposited using physical vapor deposition (PVD) or chemical vapor deposition (CVD). Preferably, a radiopaque coating comprising platinum, tungsten, iridium, tantalum or the like is deposited on a desired portion of the device. Alternatively, the performance enhancing coating is a wear resistant coating of carbides such as tungsten carbide, titanium carbide, or nitrides such as titanium nitride.

This is a continuation-in-part application of copending application Ser.No. 09/098,443, which was filed on Jun. 17, 1998, incorporated herein inits entirety by reference.

BACKGROUND OF THE INVENTION

This invention is directed to the field of intraluminal devices havingcoatings which provide radiopacity or wear resistance, and, inparticular, to guidewires or stents having these features.

In a typical coronary procedure a guiding catheter having a preformeddistal tip is percutaneously introduced into a patient's peripheralartery, e.g. femoral or brachial artery, by means of a conventionalSeldinger technique and advanced therein until the distal tip of theguiding catheter is seated in the ostium of a desired coronary artery.There are two basic techniques for advancing a guidewire into thedesired location within the patient's coronary anatomy, the first is apreload technique which is used primarily for over-the-wire (OTW)devices and the bare wire technique which is used primarily for railtype systems. With the preload technique, a guidewire is positionedwithin an inner lumen of an OTW device such as a dilatation catheter orstent delivery catheter with the distal tip of the guidewire justproximal to the distal tip of the catheter and then both are advancedthrough the guiding catheter to the distal end thereof. The guidewire isfirst advanced out of the distal end of the guiding catheter into thepatient's coronary vasculature until the distal end of the guidewirecrosses the arterial location where the international procedure is to beperformed, e.g. a lesion to be dilated or a dilated region where a stentis to be deployed. The catheter, which is slidably mounted onto theguidewire, is advanced out of the guiding catheter into the patient'scoronary anatomy over the previously introduced guidewire until theoperative portion of the intravascular device, e.g. the balloon of adilatation or a stent delivery catheter, is properly positioned acrossthe arterial location. Once the catheter is in position with theoperative means located within the desired arterial location, theinterventional procedure is performed. The catheter can then be removedfrom the patient over the guidewire. Usually, the guidewire is left inplace for a period of time after the procedure is completed to ensurereaccess to the arterial location if it is necessary. For example, inthe event of arterial blockage due to dissected lining collapse, a rapidexchange type perfusion balloon catheter such as described and claimedin U.S. Pat. No. 5,516,336 (McInnes et al), can be advanced over thein-place guidewire so that the balloon can be inflated to open up thearterial passageway and allow blood to perfuse through the distalsection of the catheter to a distal location until the dissection isreattached to the arterial wall by natural healing.

With the bare wire technique, the guidewire is first advanced by itselfthrough the guiding catheter until the distal tip of the guidewireextends beyond the arterial location where the procedure is to beperformed. Then a rail type catheter, such as described in U.S. Pat. No.5,061,395 (Yock) and the previously discussed McInnes et al., is mountedonto the proximal portion of the guidewire which extends out of theproximal end of the guiding catheter which is outside of the patient.The catheter is advanced over the catheter, while the position of theguidewire is fixed, until the operative means on the rail type catheteris disposed within the arterial location where the procedure is to beperformed. After the procedure the intravascular device may be withdrawnfrom the patient over the guidewire or the guidewire advanced furtherwithin the coronary anatomy for an additional procedure.

Conventional guidewires for angioplasty, stent delivery, atherectomy andother vascular procedures usually comprise an elongated core member withone or more tapered sections near the distal end thereof and a flexiblebody such as a helical coil or a tubular body of polymeric materialdisposed about the distal portion of the core member. A shapeablemember, which may be the distal extremity of the core member or aseparate shaping ribbon which is secured to the distal extremity of thecore member extends through the flexible body and is secured to thedistal end of the flexible body by soldering, brazing or welding whichforms a rounded distal tip. Torquing means are provided on the proximalend of the core member to rotate, and thereby steer, the guidewire whileit is being advanced through a patient's vascular system.

An important attribute for guidewires is sufficient radiopacity to bevisualized under a fluoroscope, allowing the surgeon to advance theguidewire to a desired location. Unfortunately, the most suitablematerials for guidewires, such as stainless steel, exhibit relativelylow radiopacity. Accordingly, various strategies have been employed toovercome this deficiency. Portions of the guidewire, usually theshapeable tip, may be made from or coated with relatively radiopaquemetals such as platinum, iridium, gold or alloys thereof. For example, a3 to 30 cm platinum coil tip is frequently soldered to the distal end ofthe guidewire. Other intraluminal devices such as stents may make use ofradiopaque gold plating. An obvious drawback of these prior art methodsis the high expense and scarcity of these radiopaque metals and thedifficulty and expense of manufacturing products from these materials.The requirement of both radiopacity and high strength and flexibility islikewise an impediment.

Guidewires often are used to cross hardened plaques or total occlusions.The prior art has achieved wear resistant tips, but generally only atthe expense of other desirable properties. As a result, an additionalimportant feature of guidewires is a wear resistant tip that does nototherwise constrain guidewire design.

Accordingly, there remains a need for guidewires or stents havingsufficient radiopacity to allow visualization under a fluoroscopewithout the use of expensive metals such as platinum. Additionally,there is a need for guidewires having wear resistant surfaces. Thisinvention satisfies these and other needs.

SUMMARY OF THE INVENTION

This invention comprises an intraluminal device having a performanceenhancing coating deposited using physical vapor deposition (PVD) orchemical vapor deposition (CVD).

One aspect of the invention is an intraluminal device having aradiopaque coating applied to at least a portion of the device. In apresently preferred embodiment, the intraluminal device is a stent or aguidewire, preferably formed of stainless steel, and the coating isapplied to the distal tip of the guidewire. Preferably, the radiopaquecoating may comprise platinum, tungsten, iridium, tantalum, or the like.

In another aspect of the invention, a wear resistant coating comprisingcarbides such as tungsten carbide, titanium carbide, or nitrides such astitanium nitride is applied to an intraluminal device such as aguidewire. The invention also comprises the methods of making suchintraluminal devices.

A variety of conventional guidewire and stent designs may be used, asfor example the guidewires and associated devices for variousinterventional procedures disclosed in U.S. Pat. No. 4,748,986 (Morrisonet al.); U.S. Pat. No. 4,538,622 (Samson et al.): U.S. Pat. No.5,135,503 (Abrams); U.S. Pat. No. 5,341,818 (Abrams et al.); and U.S.Pat. No. 5,345,945 (Hodgson, et al.), and stents and associated devicesdisclosed in U.S. Pat. No. 5,514,154 (Lau et al.); and U.S. Pat. No.5,476,505 (Limon), which are hereby incorporated herein in theirentirety by reference thereto.

The radiopaque or wear resistant coatings of the invention depositedonto an intraluminal device preferably have a very uniform and smoothsurface. Moreover, the coating may be extremely thin for improved deviceperformance. The hard and wear resistant coatings of the inventionprovide a variety of properties in addition to wear resistance,including radiopacity, bending stiffness, and solderability. These andother advantages of the invention will become more apparent from thefollowing detailed description and accompanying exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates guidewire of the invention with a shapeable coil tiphaving a performance enhancing coating.

FIG. 2 is a cross section of the intermediate coil of the guidewire ofFIG. 1.

FIG. 3 is a sectional detail of the shapeable coil showing theperformance enhancing coating.

FIG. 4 shows a schematic view, partially in section, of a deliverycatheter with a stent having features of the invention positioned withina body lumen.

FIG. 5 is a cross section of the delivery catheter and stent assembly ofFIG. 4.

FIG. 6 is a schematic view of the stent anchored within the bodilylumen.

FIG. 7 is a cross section of the stent of FIG. 6.

FIG. 8 is a detail view of the FIG. 7 cross section showing theperformance enhancing coating.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-3 illustrate a guidewire 10 having features of this inventionthat generally include an elongated core member 12 and a distal tip 14having a performance enhancing coating on at least a portion thereof.The distal tip 14, which may be shaped or shapeable, comprises aflexible helical coil 16 and a rounded member 18 on the distalextremity, preferably formed by a solder plug securing helical coil 16to core member 12.

In the embodiment illustrated in FIGS. 1-3, a performance enhancingcoating is located on a distal portion 22 of the helical coil 16. FIG. 3shows a detail of the distal portion 22 of helical coil 16 havinguniform performance enhancing coating 24. However, various portions ofthe guidewire may be coated as desired. As shown in section in FIG. 2,intermediate portion 20 of helical coil 16 does not have a coating, butin alternate embodiments described below it may. In a presentlypreferred embodiment, the radiopaque coating 24 is located on either thedistal 3 cm of the helical coil 16, or the distal 30 cm which includesthe intermediate coils, depending of the physician's preference.

Suitable coatings include platinum, tungsten, tantalum, iridium andother radiopaque materials to provide radiopacity for guidewire 10. Insuch embodiments, the portion of the guidewire coated with theradiopaque material is typically formed from stainless steel, nickeltitanium alloys or other materials that have relatively low radiopacity.

In another embodiment, the distal portion of guidewire 10 may have acoating to provide a hard, wear resistant surface. The wear resistantcoating is preferably a carbide or a nitride, such as tungsten carbide,tungsten nitride, titanium carbide, or titanium nitride. In a presentlypreferred embodiment, the hard and/or wear resistant coating is on thedistal end of the guidewire 10, which provides improved guidewireperformance in applications such as the crossing of total occlusions(CTO wires). Such a hard and wear resistant coating can also provideradiopacity. Additionally, the titanium carbide, titanium nitride, andother wear resistant coatings of the invention increase the rigidity andstiffness of the substrate. This enables the coated tip of the guidewireto be shaped. For example, a NiTi alloy tip-generally has poor abilityto retain a bent or curved shape. In contrast, a NiTi alloy tip having awear resistant coating of the invention would have improved bendingstiffness and shape retention. Thus, a wear resistant coating havinghigher hardness and strength compared to the substrate, such as astainless steel coating deposited on a NiTi substrate, provides aguidewire tip which retains a bent shape, i.e., a plastically shapeabletip.

Generally, the coating of this invention should be about 0.1 to about 15μm thick, and preferably about 0.5 to about 10 μm. These thin coatingsprovide uniform coverage of the helical coil without the bridgingbetween adjacent coils of prior art methods, which can interfere withperformance. Also, the coatings of this invention have a very uniformand smooth surface, offering an improved coefficient of friction.Particularly preferred coatings include radiopaque coatings of platinum,tantalum, tungsten and wear resistant coatings of tungsten carbide ortitanium nitride. Guidewires of the invention may further comprise alayer of a hydrophilic polymer. Such a hydrophilic coating over theradiopaque coating provides lubricity.

In another embodiment of the invention, shown in FIGS. 4 through 8, astent 26 is provided with a performance enhancing coating 28 on all or aportion of the surface. FIG. 4 is a schematic view of a deliverycatheter 30 mounted over a guidewire 32 and positioned within a bodilylumen 34. Delivery catheter 30 generally comprises an elongated member36 with stent 26 mounted on an inflatable member 38 designed to deformthe stent into an expanded configuration, anchoring it within lumen 34.FIG. 5 shows a cross section of the distal portion of delivery catheter30, with stent 26 mounted coaxially over inflatable member 38. As shownin FIG. 6, inflatable member 38 has been inflated, expanding stent 26 toanchor it within lumen 34. Inflatable member 38 is then deflated,allowing delivery catheter 30 to be withdrawn. FIG. 7 shows a crosssection of expanded stent 26 anchored within lumen 34 and deliverycatheter 30 with deflated inflatable member 38 being withdrawn. Finally,FIG. 8 is a detail of FIG. 7, showing performance enhancing coating 28on stent 26.

In preferred embodiments, coating 28 comprises tungsten, iridium,tantalum or the like to give stent 26 sufficient radiopacity to bevisualized under a fluoroscope. This allows the physician to confirmthat stent 26 has been properly expanded and anchored within lumen 34.In other embodiments, a different coating 28 may be suitable.

Preferably, the coating 24 or 28 is applied to helical coil 16 or stent26 by physical vapor deposition (PVD). In general, PVD involvesgeneration of the depositing species, transport of the depositingspecies to the substrate and growth of the coating on the substrate.Generation of the depositing species may be achieved either byevaporation or sputtering. In evaporative schemes, thermal energy fromresistance, induction, electron-beam or laser beam sources is used tovaporize the source material. Sputtering, on the other hand uses plasmaions generated by direct current or radio frequency to energize andeject depositing species from the source material (target) towards thesubstrate. Thus, the source material is a solid sample of the samematerial which is deposited to form the radiopaque or wear resistantcoating, such as platinum, tungsten, iridium, tantalum (forradiopacity), or carbide or a tungsten carbide (for wear resistance).The source materials are preferably biocompatible for medicalapplications. Radiopaque source materials are typically high atomicweight, high density materials, thus having a high degree of atomicabsorption. Source materials for the hard, wear resistant coatings, suchas tungsten carbide, titanium nitride, and titanium carbide, aretypically hard and often fragile materials, having a low coefficient offriction. Transport of the vaporized coating generally depends on thepartial pressure of the vaporized coating; for example molecular flowoccurs at low partial pressures while viscous flow occurs at higherpartial pressures. Depending on the technique, the substrate may also bebiased. Additionally, growth of the coating depends on the energy of thevaporized coating and substrate temperature. One of skill in the artwill be able to tailor the conditions to the type of coating beingapplied and the substrate material.

Generally preferred conditions for PVD of a radiopaque or wear resistantcoating on the distal portion of a guidewire comprise a direct current(DC) sputtering scheme with DC bias and radio frequency etch in a Alphatype vacuum chamber at about 10⁻⁵ to 10⁻⁹ Torr. The guidewires aresubjected to static deposition in which the coating is first applied toone side of the wire, and then the wire is turned 180° so that thecoating can be applied to the other side of the wire. The proximalportion of the guidewire should-be placed in a sheath to mask it fromthe PVD process, exposing only the portion where coating is desired.

SPECIFIC EXAMPLES

a) Parameters for Tungsten Coating on a Guidewire:

-   -   Voltage=610±5 volts DC    -   Power=5 kW    -   Sputtering Rate=2600 Å/min    -   Current=8.2 Amp±0.1 Amp DC

A solid sample of tungsten is used as the source material. Using theseparameters, 19 minutes are required to sputter a 5 μm thick coating oftungsten. Preferably, each layer of coating should be limited to about 5μm to prevent the temperature of the substrate from rising above about400° C. The vacuum chamber should be pumped down and subsequent layersadded via additional runs if desired. Deposition thickness is linear so10 and 15 μm thick coatings may be achieved by one or two additionalruns of equivalent time. To improve adhesion, an extremely thin 0.1 μmcoating may be deposited first. Similar conditions may be used todeposit tantalum radiopaque coatings.

b) Parameters for Wear Resistant Carbide Coatings on a Guidewire:

-   -   Voltage=625±5 volts DC    -   Power=2 kW    -   Sputtering Rate=80 Å/min    -   Current=3.15 Amp±0.05 Amp DC

These parameters will sputter a 0.25 μm thick carbide coating providingsuperior wear resistance. As above, additional runs may be used togenerate thicker coatings. A solid sample of carbide or a carbidematerial such as tungsten carbide is used as the source material.

The wear resistant performance enhancing coatings of this invention mayalso be deposited by chemical vapor deposition (CVD) processes. CVDtypically involves vaporized compounds flowing over a heated substrate.The reaction of the compounds at the substrate surface deposits a filmcoating. Preferably, CVD should be performed at low pressures to enhancethe quality of the coating.

Coatings such as tungsten carbide, titanium carbide and titanium nitridemay be prepared by a one to one proportion of the tungsten or titaniummetal, and the other element (e.g., carbon, nitrogen), before enteringthe vacuum chamber, or preferably, by using the metals as a target andintroducing a reactive gas, such as methane or nitrogen, in the chamberand allowing the metal and gas to react to form the final coatingmaterials.

The PVD and CVD processes of this invention lend themselves toautomation. Accordingly, they offer a high degree of repeatability andproduce a very uniform product. Further, the processes are faster andmore economical than conventional methods.

The invention has been described herein primarily with reference topresently preferred embodiments comprising performance enhancingcoatings applied to guidewires and stents. Other modifications andimprovements can be made to the invention and such coatings may beapplied to a variety of intraluminal products includingelectrophysiology devices, atherectomy catheters and the like withoutdeparting from the scope thereof.

1-19. (canceled)
 20. A guidewire for use in a patient, comprising: anelongated core member having a proximal core section and a distal coresection; the distal core section having a first taper, a second taper,and a third taper each of which taper in a distal direction tosuccessively smaller transverse cross-sectional dimensions therebyproviding a highly flexible distal core section; a distal coil and aproximal coil disposed about and attached to the distal core section;the distal coil having an inner portion and an exterior portion, theexterior portion being more radiopaque than the interior portion; andthe interior portion being formed from a relatively high strength metalalloy and the exterior portion being formed from a relatively lowerstrength metal or metal alloy.
 21. The guidewire of claim 20, whereinthe inner portion has a solid core in the form of a wire or a rod andthe exterior portion is in the form of a tubular member so that thetubular member can be co-drawn with the solid core to form the distalcoil.
 22. The guidewire of claim 20, wherein the inner portion is formedfrom a relatively high strength metal alloy taken from the group ofmetal alloys consisting of stainless steel, nickel-titanium,cobalt-chromium-molybdenum, and tantalum.
 23. The guidewire of claim 20,wherein the exterior portion is formed from a metal or metal alloyconsisting of platinum, gold, iridium, palladium, tantalum, tungsten,silver, and alloys thereof.
 24. The guidewire of claim 20, wherein afirst intermediate uniform dimensioned core portion extends between thefirst taper and the second taper and a second intermediate uniformdimensioned core portion extends between the second taper and the thirdtaper.